Skip to main content
NetApp Knowledge Base

What does the LUN option space_alloc do?

  1. Last updated
  2. Save as PDF
Views:
6,725
Visibility:
Public
Votes:
2
Category:
flexpod-with-infrastructure-automation
Specialty:
HW
Last Updated:

​ ​ ​  

Applies to

  • FlexPod
  • ONTAP 9

Answer

  • The space_alloc 7-mode LUN option (space-allocation in clustered Data ONTAP) allows the storage system to notify the host when it is about to run out of space in a thin provisioned environment. When the option is enabled, the storage system notifies the host through special SCSI responses when the space is out or nearly out. This allows a gentle reaction of the host to an out-of-space condition.
  • In addition, once a fully out of space condition exists for the volume containing the LUN, the LUN is left online with this option enabled. The behavior with the space_alloc option disabled is to take the LUN offline.
  • The space allocation functionality, also known as SCSI thin provisioning, uses the Logical Block Provisioning feature as defined in the SCSI SBC-3 standard. Only hosts that support this standard can use the space allocation functionality in Data ONTAP.
  • When you enable the space allocation functionality, you turn on the following thin provisioning features for standard SCSI features:
    • Unmapping and reporting space usage for space reclamation
    • Reporting resource exhaustion errors
    • Reporting low space warnings for thin provisioning thresholds

Note: Data ONTAP 8.1 and higher in the 8.1 release family support most VAAI and some Logical Block Provisioning features such as SCSI unmap, even if space_alloc is disabled. Starting in 8.2 these commands require space_alloc be enabled. LUNs with the option disabled in 8.2 will report as Thick Provisioned. 

Additional Information

N/A

NetApp provides no representations or warranties regarding the accuracy or reliability or serviceability of any information or recommendations provided in this publication or with respect to any results that may be obtained by the use of the information or observance of any recommendations provided herein. The information in this document is distributed AS IS and the use of this information or the implementation of any recommendations or techniques herein is a customer's responsibility and depends on the customer's ability to evaluate and integrate them into the customer's operational environment. This document and the information contained herein may be used solely in connection with the NetApp products discussed in this document.